Controlling the orientation and coverage of silica-MFI zeolite films by surface modification

The silica-MFI (Si-MFI) zeolite films are fabricated on α-Al2O3 supported silica–zirconia layers. The roughness and chemistry of the substrate surface are changed by surface modification with hydrogen peroxide and carboxymethyl chitosan (CMCS) solution to investigate their effects on the formation and orientation control of Si-MFI zeolite films. The AFM images reveal that the roughness of the silica–zirconia surface can be increased under the treatment of hydrogen peroxide. The Si-MFI zeolite films grown on the rough substrate surface are also b-oriented. Diffuse-reflectance FT-IR studies demonstrate that the abundance of functional groups such as –OH and –COOH can be successfully seeded onto the α-Al2O3 supported silica–zirconia layer through modification with CMCS solution. Continuous b-oriented Si-MFI zeolite films can be fabricated on the CMCS-modified α-Al2O3 supported silica–zirconia layer. It is evident that the orientation and microstructure of Si-MFI zeolite films on α-Al2O3 supported silica–zirconia layers are dominantly controlled by the chemical nature of the substrate surface, where the functional groups serve as the structure-directing matrix to induce the orientation and growth of the zeolite crystals with their b-axes perpendicular to the substrate surface.